Information retrieval and distribution systems are typically characterized by the efficiency with which they can retrieve, update and distribute vast amounts of information to authorized subscribers in real time. These systems typically utilize data acquisition and distribution techniques that permit each subscriber to access only the type of information for which it is authorized. A typical system includes a host computer having a database for collecting and storing, e.g., security and price information, from a financial/securities information source and subsequently distributing selected portions of that information to authorized users by way of a communications network. The identification of securities selected by subscribers may be entered at the host computer by a computer operator and updates to the acquired information may be periodically transmitted to the subscribers over the network. In addition, numerical values representing high and low limits of the security prices can be entered at the host so that when the price updates match the limits, the subscribers are notified. Changes to the type of information requested or to the frequency of distribution must be effectuated manually at the host and requires operator involvement, thereby increasing the cost and likelihood of erroneous entry.
Other types of known information distribution system provide a uniform wireless broadcast of data to an unlimited number of subscribers. Subscriber access is controlled by transmitted "entitlement messages" which enable the receiving means of the authorized subscribers to receive and process the broadcast data. Entitlement messages are used to provide subscribers with selected portions of data by enabling or disabling the subscriber's receiving apparatus.
Still other types of systems provide a continuously transmitted stream of encoded data messages to its subscribers. A keyword card permits a receiver and associated displaying apparatus to access the transmitted stream of data and select those of interest to be stored and displayed. Those data messages which are not of interest to the subscriber are discarded.
Each of these latter distribution systems suffers from the disadvantage that the data must be continually broadcast to all of the subscribers, resulting in the consumption of significant transmission bandwidth. Moreover, the selection, i.e., extraction, of broadcast information at each receiving unit is a significant factor in the expense of the unit, requiring expensive hardware and software components to power and outfit the unit, and to allow management of the information by the receiving unit.